Thanks Sfuhrer, we already solved it using the arming in fw mode circuit breaker and carefully adjusting the pwm disarm/min/max on both the turbine ecu and the px4 parameters, so that it allows us to manage the turbine startup in fw mode and switch in mc mode with it staying at min throttle.
Now the main issue is the vtol mc motors starting up when arming in FW. Can you please take a look at this? MC motors starts when arming VTOL in FW mode - #2 by Giovanni_Esposito Thanks!